Synchronization signal transmitter



K. SCHLESINGER 2,185,445

SYNCHRONIZATION SIGNAL TRANSMITTER Filed July 10, 1957 ZSheets-Sheet 1 Jan. 2, 1940. K. SCHLESINGER SYNCHRONIZATIDN SIGNAL TRANSMITTER Filed July 10, 1937 2 Sheets-Sheet 2 Fig.4.

In ventar:

Patented Jan. 2, 1940 UNITED STATES PATENT OFFiE SYNCHRONIZATION SIGNAL TRANSMITTER Application July 10, 1937, Serial No. 152,950 In Germany July 16, 1936 1 Claim.

The present invention relates to the production of synchronizing impulses in television transmitters in which a scanning ray of light is used.

It is already known to produce the synchronizing impulses by means of the same ray impinging an ultra-black or ultra-white edge of the image to be scanned. If, for an example, a Nipkow disc is used for scanning the same photocell and amplifier serve for taking up image contents signals and synchronization impulses.

It is one object of the invention to produce the synchronizing impulses by means of an inclined mirror disposed at one edge of the image and reflecting the ray on a second photo-cell.

Another object of the invention is to equalize the amplitude of the impulses generated by the two photo-cells.

Further objects of the invention may be best understood by reference to the following description taken in connection with the accompanying drawings in which Fig. l is a diagram of the optical and electrical arrangement,

Figs. 2a and 21) show some mechanical details, Whilst Figs. 3 and 4 show different connections for equalizing the impulse.

Referring to Fig. 1 the invention is explained on the example of a transmitter having a Nipkow disc, the scanned object being a film. Any other suitable kind of scanning device may also be used.

In Fig. 1, M is the apertured scanning disc. By means of an objective 2a, 2b a reproduction of the illuminated aperture l is produced at 1'. At this point light is passed through the film 3. Behind the latter there is arranged the image photo-cell i. This cell is connected by its anode with the input amplifier 5. When the aperture l reaches the position I" its projection 1" impinges upon the inclined mirror 6 (or a prism reflector) arranged on the edge of the frame 32 and the scanning light is reflected in the direction I. It then impinges upon the synchronization cell 8 which has the opposite polarity to the cell 4 so that its cathode is connected to the grid of the amplifier 9. Of course, at the same time only one of the two cells, either the image cell 4 or the synchronization cell 8, receives light. A mutual cross-modulation of the two groups of impulses is accordingly reliably avoided. The accuracy and linearity of a perpendicular line of the contents of the image are distinctly secured by the linearity and precision be projected on the mirror 6 and reflected on of the commencing edge of the reflector t at the point where it adjoins the film 3.

The described arrangement produces merely the line impulses. There are numerous electrical methods of producing the frame change im- 5 pulses. It would be possible, for example, to derive the frame change impulses from the alternating current mains which drive the disc I in the usual fashion by way of a synchronous motor. Since in this case, however, the inertia of 10 the disc in the case of sudden variations in frequency of the mains would cause a shifting between the rhythm of the frame and line synchronization, it is preferable to couple also the image change signals with the rotation of the Nipkow 15 disc. The same, therefore, must also be produced in mechanical-optical fashion. The image change signals are in the usual manner impulses of the same polarity and amplitude as the line signals and of a duration of one or more 20 line periods. According to the invention, they are produced in the following fashion:

In the disc I there is stamped in accordance with Fig, 2a a tangential slot I2, which lies outside of the area H scanned by the apertures, i. e. 25 on a greater radius than any of the apertures. The light passing through the slot l2 will, in the plane of the film.3, which is shown in Fig. 2b in corresponding position in relation to the disc, 0

the synchronization cell 8 (Fig. 1). The opaque vignette l3 protects the film 3 from being impinged by the light coming from the slot 12.

In order to make the intensityof the impulses produced this way approximately equal to that 35 of the line impulses there is provided a fixed opaque vignette 14 having an aperture l5 approximately equal to a scanning aperture or larger; in the latter case the light intensity may be adjusted by a grey wedge.

The intensity of the single impulses is, due to the unavoidable inequality of the apertures, varying. According to the invention the impulses are brought to the same intensity by using them for interrupting a constant current of adjustable intensity.

The method will be explained first for the transmission of negative synchronization impulses. According to Fig. 3, the mixture of synchronizing impulses is passed to an amplifying tube H, which is coupled to the output Ill of the amplifier 9. The battery 32 is connected to a resistance bridge composed on the one hand of the potentiometer l8 and on the other hand of 55.

the tube [1 with its anode resistance 19. The diagonal is formed by the diode 2| and the resistance 20, 25 being the output. In the position of rest the tube El is blocked by Way of the bias 22 and the current through tube 2i is limited by the resistances i8, i9 and 28. If the tube I? receives positive synchronizing impulses and thus becomes conductive, the anode potential of the rectifier 22 drops below the potential of its cathode. The current is interrupted, but can at no time become negative. In this way a defined, rectangular impulse signai is produced. The duration of th impulse signals at 25 is, therefore, equal to that at the grid of H, Whilst their intensity is, within far limits, independent of that of the exciting light.

In Fig. '-i there is shown a similar connection for producing positive synchronization impulses. The rectifier 2! is reversed in polarity, i. e. connected by the cathode with the anode of the tube ii. The grid of II has no bias and is provided with a high serles resistance 23 so that its potential cannot surpass zero. In the position of rest tube ll is traversed by its normal current. When negative synchronizing impulse acts on its grid the tube ii is blocked. In the same way as described above a positive impulse signal appears at 25.

The impulses at 25 arrive through a path, for example an electron tube, at the conduction between the output of the amplifier 5 amplifying the picture current of the photo-cell 3 and the modulation stage of the transmitter. In known manner this electron tube is connected in such fashion that the synchronizing impulses surpass the picture impulses or that the carrier wave is interrupted during a synchronizing impulse.

Instead of to use the output 25 there may also be arranged a reversing transformer on the place of the resistance 26. As well known in the art the synchronizing impulses may be mixed with the image signals at any proper point of the transmitter.

In certain cases the polarity of the photocells i and 8 (Fig. 1) may be exchanged. The Nipkow disc may be replaced by a lensed disc or similar scanning means.

I claim:

In a television transmitter comprising a scanning light ray, a film scanned in lines by said ray and a photo-cell behind said film connected to an amplifier, a reflecting element on one side of said film and a second photo-cell connected to a second amplifier, the output of the first mentioned amplifier and the output of the second mentioned amplifier being connected to a common terminal, one of the first mentioned elements-photo-cell and amplifierbeing opposltely poled to one of the second mentioned elements-photo-cell and amplifiersaid reflecting element projecting said scanning ray at the end of each line onto said second photo-cell, the said second amplifier being connected to a bridge, one side of which being composed by a triode and by its anode resistance, the other side of Which consisting of a potentiometer, the diagonal of which being composed of a diode and an impedance, the input of which being the grid of said triode, the output of which being tapped on said impedance.

KURT SCHLESINGER. 

